DOC-14: document Cloud topic segment size default

[micheleRP]

Resolves DOC-14.

What

Updates the Segment size row in the topic-properties table on the Cloud "Topics Overview" page (modules/develop/pages/topics/create-topic.adoc) to describe segment size qualitatively, without citing a specific value or tier-dependent limits.

Why

DOC-14 flagged that Cloud users could mistake the self-managed segment size default (1 GiB) for their Cloud value. The fix clarifies that Cloud differs, without publishing a Cloud number:

• Cloud segment size is set per cluster config profile, not a fixed 128 MiB "cluster default."

The row now states that Redpanda Cloud sets the segment size automatically and that users can override it per topic with the segment.bytes property, with no specific numbers.

Preview pages

• Topics Overview (updated)

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[coderabbitai]

📝 Walkthrough

Walkthrough

Adds a “Segment size” row to the topic properties table. The documentation describes the log segment maximum size, Redpanda’s behavior when the limit is reached, the 128 MiB cluster-level default, and per-topic overrides through segment.bytes, subject to tier-dependent limits.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Suggested reviewers: mattschumpert, kbatuigas, Feediver1

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly matches the change: documenting the Cloud topic segment size default.
Description check	✅ Passed	It includes the issue link, what/why, and a preview, with only minor template omissions like review deadline and checks.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch DOC-14-cloud-segment-size-default

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[Feediver1]

PR Review: DOC-14: document Cloud topic segment size default (#626)

Files reviewed: 1 .adoc file (modules/develop/pages/topics/create-topic.adoc)
Overall assessment: Clean, well-scoped change that closes a real content gap. One cross-repo inconsistency surfaces on a directly linked page and should be fixed in the docs repo, otherwise ready to merge.

What this PR does

Adds a Segment size row to the topic-properties table on the Cloud "Topics Overview" page. The row explains what a log segment is, states that Redpanda Cloud sets segment size automatically (deliberately without publishing a number, since the value comes from per-cluster config profiles), and notes the per-topic override via segment.bytes.

Jira ticket alignment

Ticket: DOC-14 — Document alternative segment size defaults in Redpanda Cloud
Status: Substantially addressed, with one deliberate divergence and one remaining scope item:

• The ticket asks to document the specific Cloud values (128 MiB default, 16–256 MiB bounds). The PR intentionally omits all numbers because Cloud now sets segment size per cluster config profile and customer scaling is replacing fixed tiers. This is documented in the PR body and commit history, and the SME approved — reasonable divergence, but the ticket resolution comment should record why no numbers were published.
• The ticket's original example — the self-managed disk-utilization page citing the 1 GiB default with no Cloud caveat — lives in the docs repo (modules/manage/pages/cluster-maintenance/disk-utilization.adoc) and is untouched. It doesn't render in cloud-docs, so it's arguably out of scope here, but DOC-14 shouldn't be closed as fully resolved without deciding whether that page needs a "Cloud differs" note.

Critical issues (must fix)

None in the changed file itself. But see the cross-repo finding below — it contradicts this PR's content on a page one click away.

Suggestions (should consider)

1. [create-topic.adoc: Segment size row] Every other row with configurable behavior states its default in bold ("The default is 20 MiB…"). This row can't cite a number, which is correct — but consider making the absence explicit, e.g. "The default depends on your cluster configuration," so readers don't assume the omission is an oversight. Optional; the current wording is acceptable.

Impact on other files

• docs repo, modules/develop/pages/manage-topics/config-topics.adoc (lines 306–334): The ifdef::env-cloud[] example output for rpk topic describe — which renders on the Cloud Manage Topics page, the first "Next steps" link from the page this PR edits — shows segment.bytes 1073741824 DEFAULT_CONFIG. That tells Cloud users their default segment size is 1 GiB, contradicting both this PR ("Redpanda Cloud sets the segment size for your cluster automatically") and actual Cloud behavior. The Cloud-gated example block appears to have been copied from the self-managed example without adjusting values. This needs a follow-up PR in the docs repo (the page is single-sourced into cloud-docs), either correcting the value or removing the segment.bytes line from the example.
• No What's New entry needed (clarification, not a feature), no nav or xref impact (no new or moved pages).

What works well

• The qualitative framing ("set automatically… override with segment.bytes") is future-proof against config-profile changes, and the decision not to publish numbers is well documented in the commit messages.
• The two-sentence structure (what a segment is, then the Cloud behavior) matches the pattern of the other table rows, and voice/tense/terminology are all compliant.
• The intermediate commits show the 1 GiB comparison and tier-dependent limits were consciously removed, not forgotten — good revision hygiene.

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